Our research effort is concerned with a determination of the molecular mechanisms of mixed function oxidation reactions as catalyzed by the P450 type monoxygenases. P450 hemoproteins are found ubiquitously in nature, playing a central role in the hepatic detoxification of drugs, carcinogens, and environmental pollutants. Additionally, biotransformation of cholesterol in the adrenals involves sterospecific hydroxylation reactions by P450 systems, in both cleavage of the side chain at the apex of the D ring, as well as selective ring oxygenations. Methods of procedure involve determination of the precise biochemistry and biophysics of pyridine nucleotide dehydrogenation, electron transfer, and catalytic oxygen-oxygen bond cleavage by the P450 system with prime focus on the mechanistic chemistry of substrate oxygenation, and the mode of regulation and control of xenobiotic metabolism by substrate, membrane environment, and redox equilibria.